The measurement of blood-tissue permeability in the lung has proven to be extremely difficult. We have developed a new in vitro method to measure the permeability of cultured endothelial cell layers from pulmonary arteries, veins, and microvessels. The method offers a fresh approach and overcomes many of the difficulties of whole animal methods used to study the increased permeability edema often characteristic of the adult respiratory distress syndrome. Blood-tissue permeability increases are difficult to prove in animal models of increased permeability edema. For example, investigators have such the sheep lung- lymph preparation and stimuli such as histamine, endotoxin, and thrombin as models of lung injury similar to increased permeability edema. However, blood-tissue permeability changes cannot be clearly identified in these animal models, since the lung injury is accompanied by increased intravascular pressures which could also account for the observed increased flux of fluid and solutes. In vitro methods will help identify specific permeability changes induced by agents producing lung injury in animals. Using recent advances in cell culture methods, the permeability characteristics of the endothelial component of the blood-tissue barrier have begun to be investigated. However, these results are being questioned, since these in vitro methods find permeabilities 1000 times greater than in vivo estimates. In preliminary experiments, our in vitro method finds endothelial permeabilities similar to in vivo estimates. This new method utilizes a monolayer of endothelial cells cultured on microcarrier beads as a selective barrier to control the passage of molecular species from the mobile phase of a liquid chromatography column to the stationary phase within the cell covered microcarrier beads. We propose to use this method to clarify the role of the endothelial barrier in blood-tissue permeability and, in addition, measure how the permeability properties are altered by naturally occurring stimuli, i.e. autacoids. This proposal has three main aims: 1) to measure the in vitro intercellular permeability of the pulmonary endothelial cell layer to mannitol and polyethylene glycol; 2) to characterize the permeability of the pulmonary endothelial cell layer with respect to tracer size and charge; and 3) to test the hypothesis that autacoids alter pulmonary endothelial cell permeability by measuring permeability changes produced by three autacoids, which have been described as reversible modulators of blood-tissue permeability in the lung: norepinephrine, thrombin and histamine.